Fragile X syndrome (FraX), the most prevalent form of inherited mental retardation, is associated with the absence of FMRP, a protein involved in regulation of protein synthesis. Recent microarray studies have identified transcripts that are abnormally regulated in both brains from FMRP knockout mice and lymphoblasts from males with FraX. These FMRP targets include structural and functional proteins that participate in synaptic development and plasticity. In addition, using proteomics techniques, we have demonstrated in FraX lymphocytes abnormal acetylation of several proteins that include the microglial regulatory protein annexin-1 (Anx-1) and the neuronal cytoskeletal protein a-tubulin. Abnormal Anx-1 expression is also predictive of autistic features in FraX. We hypothesize that specific aspects (e.g, autism, megalencephaly), and variability, of the FraX neurobehavioral phenotype are the consequence of abnormal expression of one or more neural proteins, and that these contributions can be identified by characterizing patterns of abnormal neural protein expression in lymphocytes and their neurobehavioral correlates in males with FraX. We propose to study the patterns of expression of 12 selected FMRP targets in lymphocytes from a well-characterized sample of males with FraX, representing the spectrum of neurobehavioral phenotypic manifestations. In Aim l, we will use a combination of immunochemical techniques to characterize patterns and levels of lymphocytic protein expression in 100 males with FraX and 20 controls. In Aim 2, we will examine the relationships between these molecular variables and selective aspects of the neurobehavioral phenotype (e.g., a-tubulin and IQ) of the FraX subjects. Since blood samples and behavioral data are available on 50 FraX and 10 control subjects, only half of the sample will be recruited over two years. Preliminary data also show the feasibility of studying 4 of the proposed proteins. Because of their innovative approach to examining genotype-phenotype relationships, we believe that the proposed studies are in accordance with the purposes of the Exploratory/Developmental Grant (R21) Program. [unreadable] [unreadable]